The present invention relates generally to systems and apparatus for processing whole blood, and more specifically to blood fractionation systems and apparatus having a filter component for separating and collecting a desired blood component, such as plasma, from whole blood through a single-lumen phlebotomy needle.
Various methods and apparatus have been developed for the in vivo processing of whole blood, wherein whole blood is taken from a donor, a desired blood component is separated and collected, and the processed blood is returned to the donor. Blood components typically collected using such processing include plasma (plasmapheresis), white blood cells (leukopheresis) and platelets (plateletpheresis).
In vivo blood processing apparatus may be of the centrifugal type, wherein the differing density of the collected blood component causes the component to congregate for collection at a particular radial distance in a centrifuge, or may be of the filter type, wherein the particle size of the collected component allows only that component to pass through a filter membrane into a collection chamber. Filter type apparatus is generally preferable for in vivo plasmapheresis applications, since such apparatus does not require complex rotating machinery and is more compact and less costly to manufacture.
One form of filter which is particularly attractive for use in plasmapheresis apparatus utilizes a plurality of parallel microporous hollow fibers arranged side-by-side in the form of a bundle within a hollow cylinder. As whole blood is caused to flow through the fibers the plasma component passes through the walls of the fibers to the surrounding container, which forms a collection chamber from which the component is transported to a collection container. A preferred construction and method of manufacture of such a flow-through hollow fiber filter is shown in the copending application of Robert Lee and William J. Schnell, entitled, "Microporous Hollow Fiber Membrane Assembly and Its Method of Manufacture", Ser. No. 278,913, filed June 29, 1981 now abandoned, continuation application Ser. No. 604,396 filed Apr. 26, 1984.
The efficiency of a flow-through filter in separating plasma from whole blood depends on the hematocrit of the donor, and the flow rate and pressure of the whole blood as it is pumped through the filter. Insufficient flow rates or whole blood pressures result in less than optimum yields. Excessive flow rates or whole blood pressures result in hemolysis, or damage to the red blood cells, within the filter, and possible failure of the filter to exclude red blood cells from the collected plasma. Thus, a practical limit exists for the percentage of plasma that can be recovered by a flow-through membrane filter in a single pass of whole blood.
To improve the efficiency of blood fractionation systems it has been proposed that once-filtered plasma-deficient whole blood be recirculated through the filter. This enables the filter to refilter the previously-filtered whole blood, recovering an additional percentage of the remaining plasma component. A blood fractionation system providing such recirculation is described in the copending application of Arnold C. Bilstad et al, entitled, "Increased Yield Blood Component Collection System and Methods", Ser. No. 411,057, filed Aug. 24, 1982 now abandoned, continuation application Ser. No. 690,399 filed Jan. 9, 1985.
However, in certain procedures, as where a high hematocrit is encountered in the whole blood drawn from a donor, the hematocrit of the once-filtered plasma-deficient whole blood may be so high as to require a reduction in the filter flow rate and pressure with an attendant reduction in filter efficiency, to avoid hemolysis in the second pass through the filter. This has the effect of increasing the time required to separate a given quantity of plasma, thereby increasing the inconvenience of the procedure to the donor. Accordingly, the need has developed for a blood fractionation system wherein recirculation through the filter is obtained while maintaining hematocrit, flow rate and pressure parameters which provide optimum system efficiency.
Furthermore, for user comfort it is desirable that in vivo blood fractionation systems withdraw and return whole blood to the donor through a single phlebotomy needle at a single injection site. This necessitates either the use of a single duallumen phlebotomy needle, in conjunction with a continuous flow non-batch system, such as described in the copending application of Arnold C. Bilstad et al, entitled "Blood Fractionation Apparatus", Ser. No. 330,898, filed Dec. 15, 1981, now U.S. Pat. No. 4,447,191, or of a single-lumen phlebotomy needle in conjunction with a bidirectional batch system, whereby batches of whole blood are alternately drawn through the needle, passed through a plasma separation filter, and returned through the same needle. Such bidirectional single-lumen batch systems have the advantage of utilizing a smaller and potentially less traumatic single lumen needle. However, since such systems have heretofore not provided plasma separation from the batch in process during both the draw and return cycles, they have undesirably prolonged the time required to collect a desired volume of plasma.
The present invention is directed to a bidirectional single-needle batch type blood fractionation system which provides for user-controlled partial recirculation of plasma-deficient whole blood through the system filter during the blood return cycle, thereby enabling optimum plasma separation efficiency to be maintained in the system notwithstanding variations in whole blood hematocrit. Basically, whole blood is drawn from the donor through a single phlebotomy needle and associated bidirectional donor conduit and pumped through the filter to a reservoir by an inlet pump. As the whole blood passes through the filter plasma is separated and stored in a separate collection container. Upon reaching a predetermined volume, filtered plasma-deficient whole blood in the reservoir is pumped from the reservoir to the donor conduit by a return pump, which operates at a higher rate than the inlet pump. By reason of the higher rate of the return pump flow is reversed in the donor conduit and a portion of the plasma-deficient whole blood is returned to the donor through the phlebotomy needle, and the remaining portion is recirculated through the filter, without the need for valves for controlling fluid flow in the system. By controlling the relative speeds of the inlet and return pumps, the portion of the plasma-deficient whole blood from the reservoir recirculated through the filter can be varied to maintain a desired hematocrit at the filter.
The present invention, by increasing the plasma separation efficiency of the system, makes a reduction in the volume of the system filter possible. This is advantageous in that it reduces the quantity of extracorporeal blood in process, and the cost of the system filter and the microporous filter material utilized therein.
Accordingly, it is a general object of the present invention to provide a new and improved fluid fractionation system for separating a fluid fraction from whole fluid.
It is a more specific object of the present invention to provide a new and improved blood fractionation system for separating plasma from whole blood.
It is a further object of the present invention to provide filter-type blood fractionation system having reduced in-process volume.
It is a further object of the present invention to provide a filter-type blood fractionation system having improved plasma separation efficiency.
It is a further object of the present invention to provide a new and improved filter-type blood fractionation system having user-controllable recirculation through the filter.
It is a further object of the present invention to provide a new and improved blood fractionation system utilizing a single lumen needle.
It is a further object of the present invention to provide a valveless single-lumen needle blood fractionation system.